Computer aided design (CAD) tools have become standard in many industries. Such tools are used in designing everything from buildings to micro-machines. Generally, designs are created in two dimensional drawings which might include various individual piece drawings as well as assembly and view drawings.
It is often useful when working with design drawings to view three dimensional representations of the objects in the drawings. Three dimensional (3D) visualization of objects is useful in a variety of contexts. For example, CAD designs can be converted to 3D representations to allow designers a better understanding of the element being designed.
Items in CAD drawings include product and manufacturing information or PMI. PMI is used to convey information on the design of a product's components for manufacturing. This includes data such as geometric dimensioning and tolerancing, 3D annotation (text) and dimensions, surface finish, and material specifications.
The PMI annotation is created on the 3D CAD model, and associated to edges and faces. Normally multiple levels of annotations are provided. This layered approach allows the user to switch between various views and have the ability to activate/deactivate each layer or any particular annotation.